Accurate estimation of an aircraft's position in the air (e.g., altitude, attitude, etc.) is very important. Some current altitude estimation techniques rely upon vision or wave-based propagation techniques, such as radar and Lidar. However, vision and wave-based altitude estimation techniques are undesirable in some applications for a variety of reasons. For example, vision and wave-based altitude estimation techniques do not sense the presence of ground effect and so would not work well for vertical takeoff and landing (VTOL) multicopters (which generate large amounts of downward airflow) when such aircraft are operating near the ground. The downward airflow acts as a cushion between the vehicle and the ground and contributes to abnormal vehicle dynamics, hence methods that accurately sense the interaction between a multicopter and the ground are crucial for successful VTOL. Another drawback to wave-based altitude estimation techniques is that wave-based systems tend to be heavy and/or expensive. New altitude estimation techniques which work in the presence of ground effect and/or which are relatively light and/or inexpensive would be desirable (e.g., for use in lightweight and/or VTOL multicopters).